1. Field of the Invention
The present invention relates to a transmission liquid crystal panel through which rays of light are transmitted downwardly from above, and more particularly to a transmission liquid crystal panel in which encapsulated liquid crystal is driven by thin film transistors in an active matrix mode.
2. Description of the Related Art
Conventionally, image displays for displaying images on a screen utilizing liquid crystal have been put to practical use as liquid crystal projectors and projection televisions. Such an image display generally includes a light source, a transmission liquid crystal panel and a screen, in which rays of light emitted from the light source is transmitted through the transmission liquid crystal panel and radiated on the screen.
FIG. 1 shows a liquid crystal light valve 100 which is a prior art of the transmission liquid crystal panel. Liquid crystal light valve 100 comprises as its main components, transparent substrate 101, numerous lower light blocking films 102, numerous TFTs (Thin Film Transistor) 103, a plurality of gate electrodes (not shown), a plurality of drain electrodes (not shown), a plurality of data electrodes 104, a plurality of upper metal films 105, planarizied layer 106, numerous separate electrodes 107, encapsulated liquid crystal 108, common electrodes 109, and opposite substrate 110.
For the sake of simplicity, in the following description xe2x80x9clower side, upper sidexe2x80x9d will designate the circuit side, the liquid crystal side, respectively in the laminating direction of the various types of the layers in liquid crystal light valve 100, as shown in FIG. 1.
Transparent substrate 101 is made of a colorless and transparent insulating glass substrate, on the surface of which, a plurality of lower light blocking films 102 are laminated. Lower light blocking films 102 are made of WSi (tungsten silicide) with high heat resistance and low light transmittance, and are formed in a layer thickness and a pattern so as to shield each of numerous TFTs 103 from stray light in an upwardly slanted direction from below.
TFT 103 is located above lower light blocking film 102 through interlayer insulating film 111, and includes a source region and a drain region formed thereon (not shown). The source region is connected to data electrode 104, while the drain region is connected to the drain electrode (not shown). The gate electrode (not shown) of TFT 103 comprises a metal layer with a pattern extending in a lateral direction in the drawing, and is located generally on the upper surface of TFT 103.
Data electrode 104 comprises an aluminum layer with a pattern extending in a direction normal to the drawing, and laminated above TFT 103 through interlayer insulating film 112. In other words, the gate electrodes and data electrodes 104 form a matrix electrode, at the intersections of which respective TFTs 103 are arranged.
Upper metal film 105 is made of a highly reflective aluminum layer laminated above data electrode 104 through interlayer insulating film 113, and is formed in such a layer thickness and a pattern as to shield data electrode 104. Planarizied layer 106 is made of insulating organic resin such as polyimide and laminated on upper metal film 105 with its upper surface being formed flat.
Each separate electrodes 107 is made of ITO (Indium Tin Oxide) layer formed on the upper surface of planarizied layer 106, and is connected to the drain electrode of TFT 103.
More specifically, as mentioned above, the gate electrodes and data electrodes 104 form the matrix electrode which is separated into numerous rectangular sections aligned in the longitudinal and transverse directions, each section corresponding to each a display pixel in a dot matrix. Each separate electrode 107 is formed for each display pixel and connected to each TFT 103 through a contact hole (not shown).
Opposite substrate 110 is also made of a colorless and transparent insulating glass substrate and is laminated above planarizied layer 106 with a predetermined gap there between through a spacer member (not shown). Common electrodes 109 are also made of an ITO layer, and are uniformly distributed on the lower surface of opposite substrate 110. Encapsulated liquid crystal 108 is made of liquid crystal encapsulated in the gap between planarizied layer 106 and opposite substrate 110, and an electric field is applied to encapsulated liquid crystal 108 with separate electrode 107 and common electrodes 109.
A peripheral circuit (not shown) is formed on the periphery of liquid crystal light valve 100 having the aforementioned laminated structure. The peripheral circuit is connected to TFTs 103 with the gate electrodes and data electrodes 104 in a matrix form. In addition, lower light blocking film 102 is grounded, and upper metal film 105 is also used as the wiring for the peripheral circuit.
Liquid crystal light valve 100 of the above configuration is utilized as part of an image display (not shown) together with a light source and a screen. In such an image display, the screen is laminated in an optical path from the light source through liquid crystal light valve 100, and rays of light emitted from the light source is irradiated on liquid crystal light valve 100 from above.
When the image display inputs image data to the peripheral circuit of liquid crystal light valve 100 at this time, the peripheral circuit outputs driving signals corresponding to the image data to TFTs 103 through the gate electrodes and data electrodes 104. TFTs 103 arranged in a matrix are individually turned with a driving voltage being then applied only to separate electrodes 107 connected to TFTs 103 turned ON.
Thus, the presence or absence of the light transmittance of encapsulated liquid crystal 108 is controlled in accordance with a dot matrix image. Rays of light transmit through liquid crystal light valve 100 from upward to downward and is irradiated on the screen, so that the dot matrix image is displayed on the screen.
In liquid crystal light valve 100 since encapsulated liquid crystal 108 is driven with TFTs 103 in the active matrix mode, the image display using liquid crystal light valve 100 can display a dot matrix image with high definition without causing crosstalk.
In the aforementioned liquid crystal light valve 100, upper metal film 105 since data electrode 104 is shielded by electromagnetic noise, which causes can also be prevented the malfunction of TFT 103, from entering data electrode 104. In addition, upper metal film 105 is also utilized as the wiring of the peripheral circuit, which need not be newly formed.
When rays of light are incident on TFT 103, includes an LDD (Lightly Doped Drain-Source) region (not shown) made of polysilicon, then leak current is generated to inhibit operational characteristics. Since the rays of light are transmitted through liquid crystal light valve 100 from above to downward, upper metal film 105 also serves to block the rays of light incident on TFT 103 from above.
In liquid crystal light valve 100 in which various types of layers are laminated, the rays of light transmitted from upward to downward may be reflected inside, and become stray light. However, lower light blocking film 102 formed below TFT 103 can prevent stray light reflected by the lower surface of transparent substrate 101 and directed toward a slant and upward direction from being entering directly on TFT 103.
However, since upper metal film 105 serving as the wiring of the peripheral circuit and as a shield for data electrode 104 is made of an aluminum film and fine gaps exist on the boundaries among particles although upper metal film 105 effectively reflects incident ray of light in reality, it is difficult to effectively block the transmission of the rays of light.
For this reason, as shown in FIG. 1, the rays of light may enter TFT 103 after they pass through upper metal film 105, which impairs the operational characteristics of TFT 103. To prevent this, the thickness of upper metal film 105 may be increased. To increase the thickness, however, deteriorates the smoothness of the upper surface of planarizied layer 106 and reduces the aperture ratio of liquid crystal light valve 100.
In addition, since data electrode 104 located above TFT 103 is also made of aluminum, it effectively reflects incident rays of light but they are difficult to effectively block its transmission. Lower light blocking film 102 is made of WSi with high heat resistance and low light transmittance which effectively reflect incident rays of light because is heated at a high temperature in the manufacturing process of TFT 103 located above lower light blocking film 102.
As a result, stray light reflected by the lower surface of transparent substrate 101 and directed toward a slant and upward direction may also enter TFT 103 after multiple reflection by the lower surface of upper metal film 105, the lower surface of data electrode 104 and the upper surface of lower light blocking film 102, impairing the operational characteristics of TFT 103.
It is an object of the present invention to provide a transmission liquid crystal panel capable of effectively preventing incidence of rays of light on thin film transistors.
It is another object of the present invention to provide an image display for effectively displaying images using the transmission liquid crystal panel according to the present invention.
It is a further object of the present invention to provide a method of manufacturing a transmission liquid crystal panel capable of effectively preventing incidence of rays of light on a thin film transistors.
According to one aspect of the present invention, a transmission liquid crystal panel comprises lower light blocking films, thin film transistors to which data electrodes, gate electrodes and drain electrodes are connected, upper metal films, a planarizied layer, separate electrodes, encapsulated liquid crystal, a common electrode, and an opposite substrate sequentially located above a transparent substrate, through which rays of light are transmitted downwardly from above. A light blocking film with lower light transmittance and lower reflectance than those of the upper metal film is formed above the thin film transistors and below the upper metal film.
In the transmission liquid crystal panel according to the present invention, the presence or absence of the light transmittance in the encapsulated liquid crystal is controlled by the thin film transistors to produce an image from light transmittance in an active matrix mode so that rays of light transmitted from upward to downward are regulated in accordance with the image. The upper metal film located above the thin film transistors limits the rays of light incident on the thin film transistor from above.
Some of the rays of light, however, are transmitted through the upper metal film. The light blocking film located below the upper metal film and above the thin film transistor has low light transmittance and blocks the rays of light transmitted through the upper metal film and directed toward the thin film transistors. In addition, since the light blocking film has low reflectance, it can prevent the ray of light transmitted through the upper metal film from becoming stray light as a result of multiple reflection by the upper surface of the light blocking film and the lower surface of the upper metal film.
A lower light blocking film with high heat resistance and low light transmittance located below the thin film transistors can prevent the rays of light reflected by the lower surface of the transparent substrate or the like from being incident directly on the thin film transistors. However, since the lower light blocking film effectively reflects the rays of light, the rays of light reflected by the lower surface of the transparent substrate or the like may be reflected by the lower surface of the upper metal film and incident on the upper surface of the lower light blocking film to become stray light which reaches the thin film transistors.
The light blocking film with low light transmittance, however, is located below the upper metal film and above the thin film transistors. Thus, the light blocking film blocks the rays of light which is reflected by the lower surface of the transparent substrate or the like and directed toward the lower surface of the upper metal film. Therefore it is possible to prevent the rays of light from becoming stray light as a result of multiple reflections by the lower surface of the upper metal film and the upper surface of the lower light blocking film. In addition, since the light blocking film has low reflectance, it can prevent the rays of light from becoming stray light as a result of multiple reflection by the lower surface of the light blocking film and the upper surface of the lower light blocking film.
For this reason, stray light with high intensity can be prevented from being incident on the thin film transistors, and the thin film transistors can be effectively operated to satisfactorily produce images in the active matrix mode.
According to another aspect of the present invention, the transmission liquid crystal panel includes the light blocking film, with lower reflectance than that of the upper metal film formed above the thin film transistors and below the upper metal film, and the light absorbing film with lower reflectance and higher heat resistance than those of the lower light blocking film formed below the thin film transistors and above the lower light blocking film.
Similarly, in the transmission liquid crystal panel of the present invention, the upper metal film located above the thin film transistors limit rays of light incident on the thin film transistors from above. In addition, the lower light blocking film with high heat resistance and low light transmittance located below the thin film transistors prevents the rays of light reflected by the lower surface of the transparent substrate or the like from being incident directly on the thin film transistors.
However, since the lower light blocking film effectively reflects the rays of light, the rays of light reflected by the lower surface of the transparent substrate or the like may be reflected by the lower surface of the upper metal film and incident on the upper surface of the lower light blocking film to become stray light which reaches the thin film transistors. The light blocking film, however, is located below the upper metal film and above the thin film transistors, as well as the light absorbing film located above the lower light blocking film and below the thin film transistors. Thus, even when the rays of light reflected by the lower surface of the light blocking film and the upper surface of the lower light blocking film is incident on the light absorbing film and the light blocking film, the light absorbing film and the light blocking film with low reflectance attenuate the incident rays of light, thereby making it possible to prevent the occurrence of stray light as a result of multiple reflection.
Therefore, stray light with high intensity can be prevented from being incident on the thin film transistors, and the thin film transistors can be effectively operated to satisfactorily produce images in the active matrix mode.
According to a further aspect of the present invention, the transmission liquid crystal panel includes the light blocking film with lower light transmittance and lower reflectance than those of the upper metal film formed above the thin film transistors and below the upper metal film, and the light absorbing film with lower reflectance and higher heat resistance than those of the lower light blocking film formed below the thin film transistors and above the lower light blocking film.
Similarly, in the transmission liquid crystal panel of the present invention, the upper metal film located above the thin film transistors limits rays of light incident on the thin film transistors from above. While some of the rays of light are transmitted through the upper metal film, the light blocking film is located below the upper metal film and above the thin film transistors.
Since the light blocking film has low light transmittance, it blocks the rays of light transmitted through the upper metal film and directed toward the thin film transistors. In addition, the low reflectance of the light blocking film can prevent the rays of light transmitted through the upper metal film from becoming stray light as a result of multiple reflection by the upper surface of the light blocking film and the lower surface of the upper metal film.
The lower light blocking film with high heat resistance and low light transmittance located below the thin film transistors can prevent the rays of light reflected by the lower surface of the transparent substrate or the like from being incident directly on the thin film transistors. However, since the lower light blocking film effectively reflects the rays of light, the rays of light reflected by the lower surface of the transparent substrate or the like may be reflected by the lower surface of the upper metal film and incident on the upper surface of the lower light blocking film to become stray light which reaches the thin film transistors.
The light blocking film, however, is located below the upper metal film and above the thin film transistors, while the light absorbing film located above the lower light blocking film and below the thin film transistors. Thus, even when the rays of light reflected by the lower surface of the light blocking film and on the upper surface of the lower light blocking film is incident on the light absorbing film and the light-blocking film, the light absorbing film and the light blocking film with low reflectance attenuate the incident rays of light, thereby making it possible to prevent the occurrence of stray light as a result of multiple reflection.
Therefore, stray light with high intensity can be prevented from being incident on the thin film transistors, and the thin film transistors can be effectively operated to satisfactorily produce images in the active matrix mode.
In an embodiment, the light absorbing film in the same pattern as that of the lower light blocking film is directly laminated on the upper surface of the lower light blocking film. In this case, the light absorbing film can reliably prevent reflection of rays of light by the upper surface of the lower light blocking film. In addition, the light absorbing film and the lower light blocking film can be simultaneously patterned in the manufacturing process to allow simple production of the transmission liquid crystal panel.
In an embodiment, the light blocking film in the same pattern as that of the upper metal film is directly laminated on the lower surface of the upper metal film. In this case, the light blocking film can reliably prevent reflection of rays of light by the lower surface of the upper metal film. In addition, the upper metal film and the light blocking film can be simultaneously patterned in the manufacturing process to allow simple production of the transmission liquid crystal panel.
In an embodiment, the light blocking film has conductivity. In this case, the upper metal film and the light blocking film can shield the data electrode to improve the shielding of the data electrode.
According to one aspect of the present invention, an image display comprises a light source, the transmission liquid crystal panel of the present invention, and a screen. In the image display of the present invention, the light source emits rays of light which is transmitted through the transmission liquid crystal panel and radiated on the screen, thereby displaying on the screen a dot matrix image produced by the transmission liquid crystal panel in the active matrix mode. Since the transmission liquid crystal panel of the present invention can effectively produce images in the active matrix mode with satisfactory operations of thin film transistors, the image display of the present invention produces images with good quality displayed on the screen.
According to one aspect of the present invention, a method of manufacturing a panel comprises the steps of, forming a first functional layer with high heat resistance and low light transmittance on the upper surface of the transparent substrate, forming a second functional layer with lower reflectance than that of the lower light blocking film on the upper surface of the first functional layer, and simultaneously patterning the second functional layer and the first functional layer to form the lower light blocking film and the light absorbing film.
In the method of manufacturing a panel according to the present invention, the light absorbing film is directly laminated on the upper surface of the lower light blocking film, and the lower light blocking film and the light absorbing film are formed in the same pattern. Thus, the method enables the production of a transmission liquid crystal panel in which the light absorbing film reliably prevents reflection of rays of light by the upper surface of the lower light blocking film, thereby making it possible to readily produce the transmission liquid crystal panel of the present invention.
According to one aspect of the present invention, a method of manufacturing a panel comprises the steps of, enclosing the data electrodes with an interlayer insulating film, forming a third functional layer with lower light transmittance and lower reflectance than those of the upper metal film on the upper surface of the interlayer insulating film, forming a fourth functional layer with high reflectance on the upper surface of the third functional layer, and simultaneously patterning the fourth functional layer and the third functional layer to form the light blocking film and the upper metal film.
In the method of manufacturing a panel according to the present invention, the light blocking film is directly laminated on the lower surface of the upper metal film, and the upper metal film and the light absorbing film are formed in the same pattern. Thus, the method enables the production of a transmission liquid crystal panel in which the light blocking film reliably prevents reflection of rays of light by the lower surface of the upper metal film, thereby making it possible to readily produce the transmission liquid crystal panel of the present invention.
In the present invention, in the laminating direction of the various types of the layers in the transmission liquid crystal panel, the circuit side is referred to as xe2x80x9clower sidexe2x80x9d and the liquid crystal side as xe2x80x9cupper sidexe2x80x9d. These directions, however, are used for the sake of convenience to simplify the description, and impose no limitation on directions during actual manufacture or use of the apparatus.
The above and other objects, features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention.